Why can't I "goto default;" or "goto case x;" within a switch selection structure?

Question

Section 6.8.1 of C11 or C99, or section 3.6.1 of C89 all seem to indicate that default and case x (where x is some constant-expression) are examples of labeled statements, along-side identifier:-style labels that are suitable for use with goto.

I'm aware that I could simply place an identifier:-style label directly following the default: or case x: labels. That's not what this question is about. I'm more curious as to whether there is any actual rationale behind prohibiting this kind of behaviour.

If it were possible to declare default: labels outside of a switch selection structure, then I would understand, as there would be some conflict between where the goto inside of the switch selection structure is intended to aim. However, section 6.4.1 of C11 or C99 or 3.1.1 of C89 prohibits the use of default as anything other than a keyword, and 6.8.1 restricts its use further to switch structures only (or generic structures in C11, which are irrelevant here).

I would also understand if multiple (possibly nested) switch structures, each with default: (or case x:) labels introduced ambiguity, however the scope of those labels seems to be restricted to within their inner-most surrounding switch structures, and referring to any identifier outside of its scope is clearly an error requiring a diagnostic at compile-time.

Has this been discussed in any standard documents (e.g. the rationale)? Is there any kind of explanation for this behaviour other than "it is because it is" or "because the spec says so"? If so, what is that explanation?

Answer 1

(I don't see how goto to a case would work syntactically.)

As you say, case and default labels only have the scope of the corresponding switch statement and can only be jumped to from outside. On the other hand labels in C have function scope and can be jumped to from anywhere in the function.

So we are talking of labels with a quite different properties, they are probably treated quite different, internally. It seems relatively complicated to reconcile these properties and would make implementing this more complicated. All of a sudden you would have to have to decide when implementing goto which case or default is the correct one, whereas now you just have to put the address of the file scope identifier, there.

All of this said, this is just a guess about the original intentions for this distinction. But I am sure that argumentation along these lines would quickly kill any attempt to introduce such a feature now.

Answer 2

counter example

fun() {
  switch (b) {
     case x:
       doSomething();
       break;
  }
  switch(b2) {
     case x:
       doMore();
       break;
  }

  goto x; // which one?
}